Orthodontic systems and methods

ABSTRACT

Orthodontic systems and methods involving segmentary shells are disclosed. Examples of the systems and methods are particularly focused on applying a distalization force to a segment of teeth in a posterior lateral sector.

This application is a 35 U.S.C. 371 filing of International ApplicationNo. PCT/EP2018/073349, filed on Aug. 30, 2018, which claims priority toand the benefit of European Patent Application No. EP 17382591.0, filedon Aug. 31, 2017, all of which are incorporated verbatim herein byreference in their entirety, including the specifications, drawings, andthe claims.

The present disclosure relates to orthodontic systems and methods, andmore particularly relates to orthodontic systems and methods usingdistalizing forces applied to a segment of teeth. The present disclosurefurther relates to removable segmentary shells.

BACKGROUND

The correction of dental irregularities and malocclusions by applyingcontrolled forces to the teeth has become commonplace. One of the mostimportant aims for orthodontics is to arrange space for teeth in the jawin such a manner that the teeth can be positioned properly and they cancontact each other in their desired positions.

So-called aligners commercialized under the name Invisalign® and underother names have become popular due to its pleasant design as comparedto traditional brackets. The treatment with aligners includes designinga treatment path for a complete arch of teeth, wherein the teeth undergoa movement from the original position to a final desired position. Then,a number of consecutive intermediate positions in between the originaland the final position for the teeth are determined, including movementsof teeth that may include rotation about a root, torsion, in-outdisplacement, and mesial-distal displacement. A series of shells (dentalsplints) is then provided to the patient. These shells correspond to thearch of teeth in their intermediate positions. The shells applycorrective forces to the arch of teeth (when fitted onto the teeth),because the shell is shaped according to the next intermediate position.Each of the shells is used during a period of time, e.g. one or a fewweeks. Once the teeth have assumed the desired position, a shellcorresponding to the next intermediate position is to be fitted. Thisprocess goes on until ultimately, the teeth reach their final desiredposition.

Some attempts have been made to improve these appliances. For example,US 2010/0075268 A1 discloses a splints system including acrylic workingplatforms and prefabricated elements constituted by a wire with acentral part that may have protuberances, loops and/or creases andundulated retention areas. The splints and the working platforms arepassive, i.e. the splints by themselves do not apply corrective forcesto the teeth. One disadvantage related to this prior solution is thatthe splints cannot be removed by a user. The acrylic working platformsare connected to the splints, and these cannot be removed withoutintervention by a professional.

US 2016/0128803 A1 discloses an aligner that comprises two shellsegments joined by a connector for covering corresponding teethsegments. This segmental aligner aims to isolate the forces betweendifferent teeth sets. However the segments are not in fact isolated,they are joined by a connector. Therefore there still exists aninteraction between the segments, with load transfer, that reduces theeffect of the corrective forces applied.

The connector in some embodiments is positioned on anterior teeth e.g.incisors in between the two shell segments. In other embodiments, theconnector is a bridge-like connector of a semi-rigid material. Theobjective of the connectors appears to be to not transfer forces fromone segment of teeth to another segment of teeth. However, even if in aninitial stage the connector does not transmit forces from one segment toanother, as soon as the segments are moved, the connector inevitablytransmits forces from one segment to the other and/or to other teeth.

Such a transmission of forces reduces the efficiency of an orthodontictreatment of the segment of teeth. A segment of teeth is herein definedas a group of neighbouring teeth, i.e. two or more neighbouring teeth.Distalization of the segment of teeth relates to moving a group of teethtogether. In particular, in the present disclosure distalization refersto moving a group of teeth in the distal direction of the mouth. Thegroup of teeth may be located in the upper jawbone (maxilla) or in thelower jawbone (mandible).

A particular distalizing element is known from e.g. EP 1 433 435 and EP1 649 824. These distalizers are especially adapted for the segmentaldistalization of the canine-to-molar posterior maxillary area. Thedistalizers of these documents comprise a mesial element which may befixed by its base to an upper canine, and further comprises a distalelement which may be fixed by its base to an upper molar, in particularthe first molar.

The mesial element in these designs comprises both a base, and an armthat connects it to the distal element. The arm may be substantiallyarch shaped and may comprise a ball member at one of its ends. This ballmember is received in a receptacle of the distal element that has acomplementary shape to the ball member.

The mesial element may comprise a blunt projection that extendssubstantially forwards which may serve as a hooking element. In use, abracket with a hook may be attached to a mandibular molar and an(orthodontic) rubber band may be suspended around this hook and thehooking element on the mesial element.

This way, a force pulling the maxillary canine backwards is provided. Ifthe patient is wearing e.g. a splint (or another fixation device) thatacts as a solid anchor and fixes the teeth of the mandible in position,it may be ensured that the teeth in the mandible do not move forwards,and that the maxillary canine is pulled backwards.

Due to the connection between the mesial element and the distal elementof the distalizer, the maxillary molar may thus also be pushedbackwards. At the same time, due to the shape of the arm in between thecanine and the molar and due to the position of the distal element onthe molar, a rotational force is also exerted upon the molar. Thisrotational force may result in a pivot about the palatal root of themaxillary molar. Also, a rotation in the distal direction of the molar(“uprighting”) may result. Thus a backwards force and a rotational forcemay be exerted upon the molar at the same time.

In order to avoid that the maxillary molar rotates too much in thedistal direction (i.e. in this case, it would assume an orientation inwhich it is tilted backwards), the shape of the receptacle and the ballmember are such that with a predetermined rotation of the ball memberwith respect to the upper molar, the ball member touches the inside ofthe receptacle and cannot rotate further. To this end, both the mesialelement and distal element are mounted at the right height on the molarand canine and are mounted substantially straight along the locallydefined mandible-maxilla (straight up-down) direction on the surface ofthe tooth. The arm is provided at a predefined angle with respect to theball member. When both the canine and molar are actually straight, thisangle will make sure that the ball member or the arm of the mesialelement touches the border of the receptacle and cannot rotate further.

Similarly, the shape of the ball member and the border of the receptaclemay be such that a rotation of the upper molar around its palatal rootis limited. Once a predetermined rotation is reached, the arm may touchthe border of the receptacle and the ball member is not able to rotatefurther.

It may thus be ensured that a distalization of the canine-molar segmentmay be combined with a proper (re)orientation of the set of teeth in themaxillary posterior region.

One drawback related to these prior art distalization devices is thatthey cannot be mounted in the mandible of many patients, because thereis not sufficient space available between molar in the mandible and aninside of a cheek of a patient. Also, when such a distalization deviceis mounted on a molar in the mandible, a molar in the maxilla couldenter into collision with the distalization device.

A further drawback related to these prior art distalization devices isthat their ability to adapt for torsion along the arm of the mesialelement is limited. Torsion along the arm may occur because e.g. a molaris inclined inwards (i.e. in the lingual direction) with respect to thecanine/premolar to which the mesial element is attached. In these cases,it is not always possible to correctly position the distalizationdevice.

Moreover, also these distalization devices are cemented on the teeth ofa patient, and so cannot be easily removed by a patient or user in aprivate setting.

There exists a need for a segmental distalization device that at leastpartially reduces some of the aforementioned drawbacks.

SUMMARY

In a first aspect, an orthodontic system is provided, which comprises aremovable segmentary shell for being fitted on a segment of teeth in aposterior lateral sector, the segment of teeth comprising between twoand six adjacent teeth and extending from a canine or premolar to apremolar or molar and a resilient traction element. Either the segmentof teeth or the removable segmentary shell comprises a labial retentionfeature configured to be coupled with the resilient traction element andthe orthodontic system is configured to apply distal forces to thesegment of teeth, without transferring the distal forces to other teethoutside the segment.

The malocclusion treatments using the segmented appliance of the presentdisclosure is able to provide a faster result than other methods. It isconfigured to apply a corrective distal force to a teeth segment inisolation, which allows focusing the corrective efforts on the segmentof teeth, making the treatment efficient and free of competitive forces.Patients can observe a faster evolution than with shells or alignersthat cover the complete dental arch and the unpleasant feeling ofwearing an orthodontic device for the duration of a treatment can bereduced to a minimum.

A shell herein may be understood as a covering that envelops either asegment of teeth (segmentary shell) or a complete arch of teeth(complete shell). In orthodontics, these types of shells may also becalled aligners, or orthodontic splints. These terms are usedinterchangeably herein.

A segmentary shell herein may be regarded as a shell element that coversonly a segment of teeth, rather than a complete arch of teeth of eitherthe mandible or maxilla.

A complete shell herein is to be regarded as a shell element that coversa complete arch either of the maxilla or of the mandible. As will beexplained later, by covering a complete arch with a shell, the reactionforce from distalization of the segmentary shell can be absorbed whilefixing the arch with respect to the jaw, i.e. without the arch movingmesially.

The shell may be made from a variety of materials, but for aestheticaspects is preferably made from a substantially transparent ortranslucent polymer. The shell might however be provided with any coloror with any desired pattern printed on the shell.

Moreover, since the shell is removable, and the traction element (whichcan be an elastic or rubber band) can be intermaxillary, a user caneasily remove the traction element and the shell without the need forintervention from a healthcare professional. This may improve usersatisfaction as, during specific social events, a user might temporarilyprefer not to wear or show orthodontic appliances.

Intermaxillary in the present disclosure means that it extends betweenthe mandible and the maxilla. I.e. the traction element may apply adistal force on a segment of teeth in the mandible by being tensionedbetween an anchor in the maxilla and the segment of teeth/shell in themandible. Alternatively, the traction element may be tensioned between aretention feature (e.g. a hook) bonded on the teeth/shell in the maxillaand an achor in the mandible.

The terms elastic band and rubber band are used interchangeably hereinand are used to denote a loop of rubber (or other elastic material),that is ring shaped. The elastic band may extend from a first hook orprotrusion (mounted with the segment of teeth) to a second hook orprotrusion provided on an anchor. By elongating the elastic band to fitaround the first and second hooks, the elastic band has a tendency toshorten and thereby provides a force to the first and second hooks.Instead of hooks, projections or protrusions around which an elasticband or other traction element could be fitted, other retention featuresthat retain a traction element might be used. Retention mayalternatively be achieved e.g. by clamping.

In some examples, the first hook (or other retention feature) may beformed or provided on the segmentary shell. In other examples, the firsthook (or first retention feature) may be attached to a tooth of thesegment of teeth, e.g. an attachment incorporating such a retentionfeature may be bonded to a surface of the tooth. In this case, the shellelement may comprise an opening, window, recess or cut-out to providespace for the first hook or projection.

The second retention feature, e.g. a second hook may be provided on ananchor, which may be a bracket provided on a tooth outside of thesegment of teeth being treated. The anchor may also be a TemporaryAnchorage Device (TAD), e.g. mounted to bone structure. Both retentionfeatures are preferably provided on a labial side of the teeth for easyaccess for the user. Yet another possibility is that a second retentionfeature is provided on or integrally formed with (a labial side of) thecomplete shell in the jaw opposite to the jaw in which the segmentaryshell is positioned.

In some examples, the segmentary shell may comprise a unilateral indentbetween two teeth of the segment, wherein the indent is oversized withrespect to a space between the two teeth, such that the indent iscompressed when the segmentary shell is positioned on the segment ofteeth. When the indent is compressed by positioning the segment on theteeth, the indent will have a tendency to open. Such a force on one sideof the segment can provide a moment to a molar which as a result canrotate around its palatal root.

In a further aspect, a method for treating a malocclusion is provided.The method includes fitting a shell to a segment of teeth in a posteriorlateral sector, the segment of teeth comprising between two and sixadjacent teeth and extending from a canine or premolar to a premolar ormolar, and applying a distal force to the segment of teeth withouttransferring the distal force to other teeth outside the segmen.

In some examples, the method may comprise providing a series ofconsecutive segmentary shells, fitting a first segmentary shell of theseries of consecutive shells to the segment of teeth, applying thedistal force to the segment of teeth with the first segmentary shellfitted on the segment of teeth for a first period of time, and replacingthe first segmentary shell with a second segmentary shell of the seriesof consecutive shells to the segment of teeth and applying the distalforce to the segment of teeth with the second segmentary shell fitted onthe segment of teeth for a second period of time.

The series of consecutive segmentary shells can apply corrective distalforces to the segment of teeth, which are independent from thedistalizing forces applied by an elastic band, i.e. these forces may bepresent if no elastic band or traction element is used. The treatmentcan be enhanced by the combination of these distalization forces of thesegmentary shells and the traction element.

In some examples, the consecutive segmentary shells substantially do notapply corrective forces other than distal forces to canine or premolars.By concentrating the treatment on distalization and postponing anymovement of canines and premolars in in-out direction, or involvingrotation etc., in a first phase of treatment, a class II o class IIImalocclusion may quickly be treated to become a class I malocclusion.After such a first stage of treatment, a second stage of treatment usinge.g. brackets or shells/aligners covering the complete dental arch maytake place. By first reducing the class II or class III malocclusion ofa class I malocclusion by focusing exclusively on distalization, aperiod necessary for the total treatment may be shortened for somepatients.

A class I malocclusion may be defined as a malocclusion in which themolar relationship is normal, but the other teeth have problems likespacing, crowding, over or under eruption. A class II malocclusion maybe defined as a situation, in which the mesiobuccal cusp of the upperfirst molar is not aligned with the mesiobuccal groove of the lowerfirst molar. Instead it is anterior to it. In a class III malocclusion,the upper molars are placed not in the mesiobuccal groove butposteriorly to it.

In some examples, one or more segmentary shells of the series ofsegmentary shells are configured to apply a rotational force to a molararound a palatal root of the molar. The rotational force may be providedby an indent as discussed before, or by including in the series ofconsecutive segmentary shells a progressing rotational movement of themolar.

In some examples, the teeth segment treated may extend from a molar to apre-molar. In some other examples, the teeth segment may extend from acanine to a molar. The molar may be a first molar, a second molar or athird molar.

In a further aspect, an orthodontic system is provided that comprises asegmentary shell configured to cover a segment of teeth in a posteriorlateral sector of either a maxilla or a mandible, and a completefixating shell configured to fit over an arch of teeth of the other ofthe maxilla and the mandible. The segmentary shell has a first surfaceand the complete fixating shell has a corresponding second surface,wherein the first surface comprises one or more first protrusions andthe second surface comprises one or more second protrusions. And thefirst and second protrusions are shaped such that when the first andsecond protrusions enter into contact, the second protrusions provide adistalization force to the first protrusions.

In this aspect, an orthodontic system is provided in which no furthertraction elements are necessary. The contact between protrusionsarranged on the segmentary shell on the one hand, and the protrusionsarranged on the complete (fixating) shell provide the distalizationforce to the segmentary shell. The segment of teeth covered by thesegmentary shell may thus undergo a distalization movement. Theprotrusions can be arranged on e.g. occlusal surfaces of the shells thatface each other, but also on either the lingual or on the labialsurfaces of the shells. The protrsuions might also be arranged on morethan one of these surfaces.

The normal ordinary movements from the mandible with respect to themaxilla throughout a day can provide repetitive contact between theprotrusions. Every time, such a contact is established, a (small)distalization force is applied to the segmentary shell. As explainedbefore, since the complete fixating shell covers a complete arch, themesial force applied onto the complete shell does not result in amovement of a segment of teeth or the complete arch of teeth (withrespect to the jaw) in the mesial direction.

The shells (segmentary and complete) may be shaped such as to fitsubstantially exactly over the corresponding teeth, including e.g. localirregularities on individual teeth of a patient. The shells may be basedon e.g. a computer model of the teeth of a patient. To this model, thenthe suitably shaped protrusions can be added which are provided with thegoal to come into contact with the protrusions on the other shell.

In some examples, the first protrusions may have a first sloping surfaceextending between a first base and a first top edge, the first top edgebeing located distally with respect to the first base. Similarly, insome examples, the second protrusions have a second sloping surfaceextending between a second base and a second top edge, the second topedge being located mesially with respect to the second base. These areexamples of shapes of protrusions that can provide a distalization forceon the segmentary shell.

“Top” herein may be understood as a portion closer to the opposing jaw.I.e. if the (segmentary or complete) shell is fitted in the maxilla,then the top of the shell is a portion that is closest to the mandible.If the shell is fitted in the mandible, then the top of the shell is aportion that is closest to the maxilla.

In some examples, the first sloping surface and the second slopingsurface are substantially complementary to each other. In otherexamples, the shapes of the protrusions can be different.

In some examples, the segmentary shell (with protrusions) or the segmentof teeth may furthermore comprise a first retention feature forreceiving a first end of a resilient traction element, the orthodonticsystem further comprising an anchor for receiving a second end of theresilient traction element, wherein the first retention featureoptionally is a hook. Even if the shells in this orthodontic system donot necessarily need a further traction element to provide adistalization force, such a traction element can provide an additionaldistalization force.

In some examples, the orthodontic system (with protrusions on theshells) comprises a series of consecutive segmentary shells, wherein thesegmentary shells are configured to apply a corrective distal force tothe segment of teeth, and wherein the consecutive segmentary shells ofthe series are shaped to correspond to consecutive positions of thesegment of teeth in a desired treatment. The series of shells may bedesigned such that the first protrusions substantially maintain theirpositions. Alternatively, the first protrusions in consecutive shellsmay be in different positions. In some examples, the orthodontic systemmay further comprise a series of complete fixating shells with varyingpositions of second protrusions.

Also in the case of shells with protrusions, a series of segmentaryshells corresponding to intermediate positions may be provided toprovide additional distalization force and thus additional speed in thetreatment. In order to ensure continued contact between the protrusionson the segmentary shell and the protrusions on the complete fixatingshell, a series of complete fixating shells may also be provided. In theseries of complete shells, the spaces corresponding to the teeth of thepatient may stay substantially the same, but the positions of theprotrusions may vary.

In a further aspect, a removable segmentary shell for being fitted on asegment of teeth in a posterior lateral sector of a maxilla is provided.The segment of teeth comprises between two and six adjacent teeth andextends from a canine or premolar to a premolar or molar. The segmentaryshell comprises one or more protrusions having a sloping surfaceextending between a base, and a top edge, the top edge being locatedcloser to the mandible than the base, wherein the top edge is locateddistally with respect to the base.

In yet a further aspect, a removable segmentary shell for being fittedon a segment of teeth in a posterior lateral sector of the mandible isprovided. The segment of teeth comprises between two and six adjacentteeth and extending from a canine or premolar to a premolar or molar.The segmentary shell comprises one or more protrusions having a slopingsurface extending between a base, and a top edge, the top edge beinglocated closer to the maxilla than the base, wherein the top edge islocated distally with respect to the base.

BRIEF DESCRIPTION OF THE DRAWINGS

Particular examples of the present disclosure will be described in thefollowing by way of non-limiting examples, with reference to theappended drawings, in which:

FIGS. 1a and 1b illustrate some of the terminology used herein;

FIGS. 2a-2c illustrates examples of segmentary shells and orthodonticsystems comprising such segmentary shells;

FIGS. 3a-3c illustrate further examples of segmentary shells which maybe used in methods and systems as herein disclosed;

FIG. 4 schematically illustrates an example of a series of segmentaryshells which may be used in methods and systems as herein disclosed; and

FIGS. 5a-5d schematically illustrate further examples of orthodonticsystems comprising a segmentary shell and a complete shell havingprotrusions.

DETAILED DESCRIPTION OF EXAMPLES

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

FIG. 1a schematically illustrates the arrangement of teeth in the lowerjaw (mandible). A front portion of the mouth 110 may be referred to as amesial region. A rear portion of the mouth 120 may be referred to as adistal region. In orthodontics, mesial and distal are terms used torefer to something being respectively closer to and further away from acentral midline of the arch of teeth.

An inner portion of the mouth behind the teeth 130 may be referred to asa lingual region (a region in which the tongue is located). An outerportion of the mouth 140 may be referred to as a labial region (a regionin which the lips are located). A mesial-distal direction 115 withrespect to a specific tooth (first molar) has been schematicallyindicated in FIG. 1. Also indicated in FIG. 1 is a lingual-labialdirection 135 with respect to the same tooth. This terminology will beadhered to in the present disclosure.

Even though a mandible is illustrated in this particular figure, itshould be clear that the same terminology applies to the maxilla.

FIG. 1b schematically illustrates a molar. A mesial side of the molar isindicated by reference sign 110 (closer to a midline of the arch ofteeth), whereas a distal side of the molar is indicated with referencesign 120 (further away from the midline). Reference signs 130 and 140respectively indicate the lingual and labial sides (or surfaces) of themolar. Reference sign 150 indicates the occlusal surface of the tooth.An occlusal surface of a tooth in the maxilla (upper jaw) faces anocclusal surface of a tooth in the mandible and vice versa.

FIG. 2a illustrates an example of an orthodontic system. The systemcomprises a segmentary shell 10 for being placed on a teeth segment. Thesegment in this example extends from a canine 31 to a molar 33 in themandible 22. The segmentary shell may be designed for each patientspecifically, i.e. the shell may be manufactured to fit substantiallyexactly around a patient's teeth taking into account e.g. smallirregularities on individual teeth and deviations of individual teeth.The shell may preferably be made of an elastic, semi-rigid or rigidtransparent or translucent material.

The segmentary shell 10 in this example comprises a hook 16 on a labialsurface of the shell. A rubber band may be fitted around this hook 16and around a second hook 14. In this example, the second hook 14 may beprovided on an attachment 17 in the complete fixating shell, the hook inthis case being arranged close to a molar 43 in the maxilla 20. As therubber band 12 is elongated, the rubber band applies a distalizationforce to the segmentary shell 10. Because the shell 10 encompasses thesegment from the canine 31 to molar 33, the distalization is transmittedto the segment.

FIG. 2b schematically illustrates another view of the segmentary shell10.

Particularly advantageous is the fact that the segmentary shell does notcover the complete dental arch, and that it is provided for only a teethsegment. There is no connection between the shell and anterior teeth orother teeth in the mandible. Thanks to this configuration, the appliancedisclosed is able to focus the corrective forces on the misaligned teethof the segment. This force concentration has the effect of providingfaster results and the overall treatment time can therefore be reduced.Other attempts to provide orthodontic appliances in the form of shellelements covering a complete dental arch cannot provide results asquickly.

It is important to avoid force transfer between the segmentary shell andother portions of the same arch, or other segmentary shell elements usedin the treatment, as they would exert a distorting negative influence inthe applied corrective forces, and can partially or completelyneutralize the intended correction, which can finally lead to a slowingdown of the treatment.

At the same time, a mesial force is applied to the molar 43 in themaxilla. In order to avoid mesial movement of the molar 43 and otherteeth in the maxilla, a complete fixating shell or splint that acts asan anchor to the maxillary teeth may be worn by a patient. This completeshell includes the entire arch of the maxilla (in this case) and extendsfrom the distal side of the last molars to the mesial side of theanterior teeth. This way any forward movement of the teeth in themaxilla with respect to the maxilla can be avoided.

In the example of FIG. 2a , the segmentary shell is applied to aposterior segment in the mandible. However, in other examples thesegmentary shell may be applied to a posterior segment in the maxilla.In this case, the anchor for the elastic band may be part of a bracketcemented on e.g. a molar or premolar in the mandible. And in that case,a shell covering the entire arch of the mandible may be provided so asto avoid movement in the mandible. This case is illustrated e.g. in FIG.2 c.

In FIG. 2c , the segmentary shell 10 in the maxilla 20 has a hook orprotrusion on the segmentary shell. A resilient traction element may bedisposed between first hook 16 and second hook 14. In the exampleillustrated in FIG. 2c , the complete fixating shell 30 has a cut-out 25arranged with a premolar in the mandible 22. This premolar carries abracket 17 with a second hook 14.

Other anchors such as TADs fitted to a bone may also be used in furtherexamples. In the examples shown, the hook (or some sort of otherprojection or protrusion) may be part of the segmentary shell 10. Inother examples, the hook may be attached to a tooth of the segment. Thesegmentary shell may comprise an opening, recess, cut-out or windowthrough which the hook protrudes.

In the examples of FIGS. 2a and 2c , the hook is shown at the positionof the canine, near a proximal end of the shell. In other examples, thehook may be provided e.g. midway along the length of the shell, eitheron the segmentary shell itself or on e.g. a premolar.

In some variations, the segmentary shell element may comprise differenttypes of retention feature for being pulled by the elastic band. Theseshapes could be any suitable protrusion shaped such that an elastic bandcan be attached, such as for instance an L-shaped protrusion, a hook orhitch among others. Also a discontinuity like a cut, a flap, a strip orthe like, would suffice for performing this function.

FIG. 3a schematically illustrates another example of a segmentary shell10 adapted to be fitted over a segment of teeth, in particular a segmentteeth in a posterior jawbone sector. The segmentary shell 10 maygenerally be similar to the shell 10 shown in FIG. 2.

In this example however, the shell comprises a unilateral indent 18 in aregion between two teeth, in particular a molar 33 and a neighbouringtooth which may be another molar or premolar. The unilateral indent isprovided on the labial side 140 of the segmentary shell. The indent maybe shaped and sized slightly larger than the available space between theteeth.

When the shell is fitted over the teeth, the indent is slightlycompressed. In use, the indent thus has the tendency to open whichapplies a rotational force to molar 33 which as a result can pivotaround its palatal root. The bottom of the indent thus has a hinge likefunction, enabling a movement of a posterior portion of the shell 10with respect to a more proximal portion of the shell.

By choosing an appropriate indent shape and size it is possible tocontrol the shell stiffness in this region and by designing the shellprofile is possible to define the deformation necessary for positioningthe aligner in the patient's teeth. The molar to which a rotationalforce may be applied may be a first molar.

FIG. 3b shows another example of a shell configured to be fitted over asegment of teeth. The shell is similar to the shell shown in FIG. 3a .In this case, a bottom 19 of the indent may include further recessesextending slightly diagonally and slightly mesially. Such recessesweaken the shell and the hinge function of the indent may be adjusted inaccordance with circumstances. In this figure (and in other figures),the segmentary shell is not shown with any sort of retention feature forretaining a traction element. It should be clear that in all suchexamples, such retention features may indeed be provided on thesegmentary shell or on teeth covered by the segmentary shell.

FIG. 3c schematically illustrates another example of a segmentary shell.In this example the segmentary shell has a first indent 18 on a labialside 140 of the segmentary shell and a second indent 28 on a lingualside of the segmentary shell. In particular, the first indent may bearranged between a premolar 51 and a first molar 53, whereas the secondindent may be arranged between the first molar 53 and the second molar55.

As explained before, the indents are compressed when the segmentaryshell is fitted to the segment of teeth. The first indent on the labialside and the second indent on the lingual side together provide arotational force on the first molar. A smaller rotational force in theopposite direction may be exerted on the premolar. But since thepremolar is in contact with the teeth mesial from it, this rotationalforce will not lead to an actual noticeable rotation of the premolar.The second molar might undergo a small rotational movement, but thispotential movement is less important in the treatment of themalocclusion than a correct rotational position of the first molar.

In a method of treatment, a scan or photos of teeth of patient may bemade so that an original situation of the teeth may be registered. Basedon the malocclusion, a treatment plan may be devised for the teeth toreach a final desired position. The final desired position mayeffectively be a final stage of a treatment. However, in other examples,the final stage of a first treatment of the segment may be the beginstage for another treatment. For example, a first treatment may startwith a class II malocclusion, whereas the treatment of the segment endswith a class I malocclusion. A second treatment may include traditionalbrackets, or shells covering a complete arch such as for exampleInvisalign®.

The method includes fitting a shell to a segment of teeth in a posteriorlateral sector, and applying a distal force to the segment of teethwithout transferring the distal force to other teeth. The wholetreatment may be done with a single shell. In other examples, a numberof intermediate situations between the original situation and the finaldesired situation may be determined. These intermediate situations maybe calculated based on a computer model of the patient's teeth. A seriesof consecutive shells may be manufactured, wherein consecutive shellssubstantially correspond to the intermediate situations. Each of theconsecutive shell segments may be worn by a patient during a period oftime, e.g. a week, or two weeks. After the period of time has passed, ashell is substituted by a consecutive shell corresponding to the nextintermediate situation.

Each of the shells can apply corrective forces to the segment of teeth,independent from the distalizing forces applied by a traction element,e.g. an elastic band. Preferably, in a first stage of treatment, onlydistal forces are applied to the canine, and premolars. Rotationalforces may only be applied to the (first) molar.

In some examples, one or more shells of the series of shells areconfigured to apply a rotational force to a (first) molar around apalatal root of the molar. The rotational force may be provided by anindent as discussed before, or by including in the series of consecutiveshells a progressing rotational movement of the molar. This has beenschematically illustrated in FIG. 4. A plurality of shells withincreased rotation of molar 33 may be provided. Whereas theuninterrupted line may indicate a first segmentary shell, theinterrupted line indicates a segmentary shell 10B further along in thetreatment.

In an aspect of the present disclosure, a treatment may involve the useof several rubber bands to vary the amount of force exerted. However theelastic element may have any other configuration suitable for itspurpose, the elastic element could also be formed by a spring, a wire orany other suitable element.

FIG. 5a schematically illustrates an example of a segmentary shellaccording to a further aspect of the present disclosure. The segmentaryshell 10 is shown to be fitted over a segment of teeth in the maxilla20. In this example, the segmentary shell comprises first protrusions 60and 60 A. Both these protrusions in this example have a sloping (i.e.inclined surface). Such protrusions 60 and 60A may be contacted bycorresponding second protrusions on a shell in the mandible, as will beillustrated in FIGS. 5b-5d showing cross-sectional views of segmentaryand complete shells.

In the example of FIG. 5b , segmentary shell 10 has protrusions 60 and60A extending from an occlusal surface 61. The occlusal surface 61 ofthe segmentary shell in use faces the occlusal surface 71 of completeshell 30. The protrusions 60 and 60A have a sloping surface 62 which inthis case is substantially straight and flat, i.e. of constantinclination. The sloping surface extends from a base at the occlusalsurface 61 towards a top edge 66, i.e. an edge closer to the mandible.The top edge is located more distal than the base.

In this example, the sloping surface 72 of the protrusions 70 and 70Ahave a substantially complementary shape to the sloping surfaces 62 ofthe protrusions 60 and 60A, i.e. the sloping surfaces fit well on top ofeach other. The sloping surface 72 is also substantially straight andextends from a base 74 at the occlusal surface to the top edge 76, i.e.closer to the maxilla. The top edge is located more mesial than thebase.

When a patient wears the segmentary shell and the complete shell, theprotrusions will repeatedly enter into contact as a patient opens andcloses his/her mouth (indicated with arrows on the right hand side ofthe figure). Whenever contact is established, the second protrusionsexert a distalization force (indicated with an arrow on the left handside of the figure) onto the first protrusions and thereby to thesegment of teeth in the maxilla.

Since the complete fixating shell covers a complete arch of the mandiblefrom behind the last molar to before the front surface of the incisors,the teeth in the mandible will not perform a mesial movement.

As illustrated in FIG. 5b , in some examples, the top edge of the secondprotrusions may be located slightly distally with respect to the base ofthe first protrusions. Similarly, the base of the second protrusions maybe located slightly distally with respect to the top of the firstprotrusions. The relative displacement of the first protrusions withrespect to second protrusions allows a relative sliding movement of apair of first and second protrusions as the patient closes his/her mouthduring which the second protrusions move (relatively) in a mesialdirection and the first protrusions move in a distal direction.

FIG. 5c illustrates a further example of a segmentary shell and acomplete fixating shell with first and second protrusions respectively.The functioning of the shells and the protrusions may generally besimilar to the example explained in FIG. 5c . However in the example ofFIG. 5c , the first and second protrusions do not have substantiallystraight/flat sloping surfaces. Rather, one or more of the firstprotrusions 60, 60A may be substantially concave. One or more of thesecond protrusions 70, 70A have sloping surfaces 72 that aresubstantially convex.

The concavities and convexities in this example are shaped as partcircular sectors, and the sloping surfaces are substantiallycomplementary but the present disclosure is not limited in that way. Thesecond protrusions in this example are again arranged slightly distallywith respect to the first protrusions so that the protrusions can movehorizontally relative to each other as the patient closes or openshis/her mouth.

In further non-illustrated examples, the first and the secondprotrusions may both be convex.

It should be clear that not all the first protrusions have to have thesame shape. Similarly, not all the second protrusions have to have thesame shape necessarily. For example, a segmentary shell might includeone or more of the first protrusions as shown in FIG. 5b and one or moreprotrusions as shown in FIG. 5c . Similarly, the complete shell mightinclude second protrusions as shown in FIG. 5b and one or more secondprotrusions as shown in FIG. 5 c.

FIG. 5d schematically illustrates yet a further example. In thisexample, the first and second protrusions do not have complementarysurfaces. The first protrusions have sloping surfaces that aresubstantially straight, and the second protrusions are substantiallycurved, and in particular convex. The second protrusions 70, 70A can“roll” over the first protrusions 60, 60A as they enter into contact,thereby providing a distlization force onto the first protrusions, thesegmentary shell, and thus the segment of teeth.

Even though in all examples of FIGS. 5a-5d , the segmentary shell isprovided in the maxilla and the complete fixating shell is provided inthe mandible, and this arrangement is particularly suitable for treatinga class II malocclusion. Instead for treating a class III malocclusion,the segmentary shell may be provided in the mandible, and the completeshell may be provided in the maxilla. A distalization force may beprovided onto the segmentary shell. The shapes of the protrusions mightbe mirrored as to the shapes shown in the previous figures. Inparticular, the base of a sloping surface may be arranged mesially withrespect to a top edge of a sloping surface.

In any of the orthodontic systems, devices and methods disclosed herein,a treatment may in some examples be asymmetric, focusing only on eithera right side or a left side of the mouth of a patient.

For reasons of completeness, various aspects of the present disclosureset out in the following numbered clauses:

Clause 1. An orthodontic system comprising:

a removable segmentary shell for being fitted on a segment of teeth in aposterior lateral sector, the segment of teeth comprising between twoand six adjacent teeth and extending from a canine or premolar to apremolar or molar; and

a resilient traction element, wherein

either the segment of teeth or the removable segmentary shell comprisesa labial retention feature configured to be coupled with the tractionelement; and wherein

the orthodontic system is configured to apply distal forces to thesegment of teeth, without transferring the distal forces to other teethoutside the segment.

Clause 2. The orthodontic system according to clause 1, wherein thesegmentary shell comprises an opening, and a tooth of the segment ofteeth comprises the labial retention feature for receiving the resilienttraction element, wherein the retention feature optionally is a hook.

Clause 3. The orthodontic system according to claim 1, wherein the shellcomprises the labial retention feature for receiving the resilienttraction element, wherein the retention feature optionally is a hook.

Clause 4. The orthodontic system according to any of clauses 1-3,further comprising an anchor for receiving the resilient tractionelement.

Clause 5. The orthodontic system according to clause 4, wherein theanchor is a bracket configured for mounting on a tooth.

Clause 6. The orthodontic system according to any of clauses 1-5,wherein the segmentary shell comprises a first unilateral indent betweena first pair of teeth of the segment, wherein the first indent isoversized with respect to a space between the first pair of teeth, suchthat the first indent is compressed when the shell is positioned on thesegment of teeth.

Clause 7. The orthodontic system according to clause 6, wherein thefirst unilateral indent is an indent on a labial side.

Clause 8. The orthodontic system according to clause 6 or 7, wherein thefirst pair of teeth of the segment include a premolar and a first molar.

Clause 9. The orthodontic system according to any of clauses 6-8,wherein the segmentary shell comprises a second unilateral indent on aside opposite to the unilateral indent and between a second pair ofteeth of the segment, wherein the second indent is oversized withrespect to a space between the second pair of teeth, such that thesecond indent is compressed when the shell is positioned on the segmentof teeth.

Clause 10. The orthodontic system according to clause 9, wherein thesecond pair of teeth of the segment are a first molar and a secondmolar.

Clause 11. The orthodontic system according to any of clauses 1-10,further comprising a fixating complete shell covering a complete dentalarch of either the maxilla or mandible.

Clause 12. The orthodontic system according to clause 11, wherein thefixating complete shell includes a hook for receiving the resilienttraction element.

Clause 13. The orthodontic system according to any of clauses 1-12,wherein the resilient traction element is an elastic band.

Clause 14. The orthodontic system according to any of clauses 1-13,comprising a series of consecutive segmentary shells, wherein thesegmentary shells are configured to apply a corrective distal force tothe segment of teeth, and wherein the consecutive segmentary shells ofthe series are shaped to correspond to consecutive positions of thesegment of teeth in a desired treatment.

Clause 15. The orthodontic system according to clause 14, wherein theseries of consecutive segmentary shells substantially do not applycorrective forces other than distal forces to canine or premolars.

Clause 16. The orthodontic system according to clause 14, wherein one ormore shells of the series of segmentary shells are configured to apply arotational force to a molar around a palatal root of the molar, whereinoptionally the molar is a first molar.

Clause 17. The orthodontic system according to any of clauses 1-16,wherein the segment extends from a canine to a molar.

Clause 18. The orthodontic system according to any of clauses 1-16,wherein the segment extends from a premolar to a molar.

Clause 19. The orthodontic system according to any of clauses 1-18,wherein the segmentary shell is substantially transparent ortranslucent.

Clause 20. A method for treating a malocclusion, including

fitting a removable segmentary shell to a segment of teeth in aposterior lateral sector, the segment of teeth comprising between twoand six adjacent teeth and extending from a canine or premolar to apremolar or molar,

applying a distal force to the segment of teeth without transferring thedistal force to other teeth outside the segment.

Clause 21. The method according to clause 20, wherein applying a distalforce includes providing a resilient traction element between an anchorand the segmentary shell or an attachment bonded to a tooth of thesegment of teeth.

Clause 22. The method according to clause 21, wherein the segmentaryshell comprises an opening, and a tooth of the segment of teethcomprises a retention feature for receiving the resilient tractionelement, wherein the retention feature optionally is a hook.

Clause 23. The method according to clause 21, wherein the segmentaryshell comprises a retention feature for receiving the resilient tractionelement, wherein the retention feature optionally is a hook.

Clause 24. The method according to any of clauses 21-23, wherein theanchor is a bracket mounted on a tooth, or a temporary anchorage device.

Clause 25. The method according to any of clauses 20-24, furthercomprising fitting a fixating complete shell covering a complete dentalarch of a jaw in which the segmentary shell is not fitted.

Clause 26. The method according to clause 25, wherein the fixatingcomplete shell includes a hook for receiving the resilient tractionelement.

Clause 27. The method according to any of clauses 20-26, wherein theresilient traction element is an elastic band.

Clause 28. The method according to any of clauses 20-27, wherein thesegmentary shell comprises a first unilateral indent between a firstpair teeth of the segment, wherein the first indent is oversized withrespect to a space between the first pair of teeth, such that the firstindent is compressed when the shell is positioned on the segment ofteeth.

Clause 29. The method according to clause 28, wherein the first indentis an indent on a labial side.

Clause 30. The method according to clause 25 or 26, wherein the firstpair of teeth include a premolar and the first molar.

Clause 31. The method according to any of clauses 28-30, wherein thesegmentary shell comprises a second unilateral indent on a side oppositeto the first unilateral indent and between a second pair of teeth of thesegment, wherein the second indent is oversized with respect to a spacebetween the pair of teeth, such that the second indent is compressedwhen the shell is positioned on the segment of teeth.

Clause 32. The method according to clause 31, wherein the second pair ofteeth of the segment are a first molar and a second molar.

Clause 33. The method according to any of clauses 20-32, comprisingproviding a series of consecutive segmentary shells,

fitting a first segmentary shell of the series of consecutive segmentaryshells to the segment of teeth, applying the distal force to the segmentof teeth with the first segmentary shell fitted on the segment of teethfor a first period of time,

replacing the first segmentary shell with a second segmentary shell ofthe series of consecutive shells to the segment of teeth and applyingthe distal force to the segment of teeth with the second segmentaryshell fitted on the segment of teeth for a second period of time.

Clause 34. The method according to clause 33, wherein the consecutivesegmentary shells are shaped to correspond to consecutive positions ofthe segment of teeth in a desired treatment.

Clause 35. The method according to clause 33 or 34, wherein theconsecutive segmentary shells are configured to apply a correctivedistal force to the segment of teeth.

Clause 36. The method according to clause 35, wherein the series ofconsecutive segmentary shells substantially do not apply correctiveforces other than distal forces to canine or premolars.

Clause 37. The method according to clause 35 or 36, wherein one or moresegmentary shells of the series of shells are configured to apply arotational force to a molar around a palatal root of the molar.

Clause 38. An orthodontic system comprising

a segmentary shell configured to cover a segment of teeth in a posteriorlateral sector of either a maxilla or a mandible,

a complete fixating shell configured to fit over an arch of teeth of theother of the maxilla and the mandible,

wherein the segmentary shell has a first surface and the completefixating shell has a corresponding second surface,

wherein the first surface comprises one or more first protrusions

and the second surface comprises one or more second protrusions,

wherein the first and second protrusions are shaped such that when thefirst and second protrusions enter into contact, the second protrusionsprovide a distalization force to the first protrusions.

Clause 39. An orthodontic system according to clause 38, wherein thefirst surface is an occlusal surface of the segmentary shell and thesecond surface is an occlusal surface of the complete fixating shellfacing the first surface.

Clause 40. An orthodontic system according to clause 38 or 39, whereinthe first surface is a lingual surface of the segmentary shell and thesecond surface is a lingual surface of the complete fixating shell.

Clause 41. An orthodontic system according to any of clauses 38-40,wherein the first surface is a labial surface of the segmentary shelland the second surface is a labial surface of the complete fixatingshell.

Clause 42. An orthodontic system according to any of clauses 38-41,wherein the first protrusions have a first sloping surface extendingbetween a first base and a first top edge, the first top edge beinglocated distally with respect to the first base.

Clause 43. An orthodontic system according to any of clauses 38-42,wherein the second protrusions have a second sloping surface extendingbetween a second base and a second top edge, the second top edge beinglocated mesially with respect to the second base.

Clause 44. An orthodontic system according to clause 42 and 43, whereinthe first sloping surface and the second sloping surface aresubstantially complementary to each other.

Clause 45. An orthodontic system according to clause 44, wherein thesecond top edge is distally displaced with respect to the first base.

Clause 46. An orthodontic system according to clause 44 or 45, whereinthe first sloping surface and the second sloping surface aresubstantially straight.

Clause 47. An orthodontic system according to clause 44 or 45, whereinthe first sloping surface is substantially concave, and the secondsloping surface is substantially convex.

Clause 48. An orthodontic system according to clause 44 or 45, whereinthe second sloping surface is substantially concave, and the firstsloping surface is substantially convex.

Clause 49. An orthodontic system according to any of clauses 38-48,wherein the segmentary shell or the segment of teeth comprises a firstretention feature for receiving a first end of a resilient tractionelement, the orthodontic system further comprising an anchor forreceiving a second end of the resilient traction element, wherein thefirst retention feature optionally is a hook.

Clause 50. The orthodontic system according to any of clauses 38-49,comprising a series of consecutive segmentary shells, wherein thesegmentary shells are configured to apply a corrective distal force tothe segment of teeth, and wherein the consecutive segmentary shells ofthe series are shaped to correspond to consecutive positions of thesegment of teeth in a desired treatment.

Clause 51. The orthodontic system according to clause 50, wherein theseries of consecutive segmentary shells substantially do not applycorrective forces other than distal forces to canine or premolars.

Clause 52. The orthodontic system according to clause 50 or 51, furthercomprising a series of complete fixating shells with varying positionsof second protrusions.

Clause 53. The orthodontic system according to any of clauses 38-52,wherein the segment extends from a canine to a molar.

Clause 54. The orthodontic system according to any of clauses 38-53,wherein the segment extends from a premolar to a molar.

Clause 55. A removable segmentary shell for being fitted on a segment ofteeth in a posterior lateral sector of a maxilla, the segment of teethcomprising between two and six adjacent teeth and extending from acanine or premolar to a premolar or molar, wherein the segmentary shellcomprises one or more protrusions having a sloping surface extendingbetween a base, and a top edge, the top edge being located closer to themandible than the base, wherein

the top edge is located distally with respect to the base.

Clause 56. A removable segmentary shell according to clause 55, whereinthe sloping surface is substantially straight.

Clause 57. A removable segmentary shell according to clause 55, whereinthe sloping surface is substantially concave.

Clause 58. A removable segmentary shell according to clause 55, whereinthe sloping surface is substantially convex.

Clause 59. A removable segmentary shell according to any of clauses55-58, wherein the protrusions are provided on an occlusal surface ofthe segmentary shell.

Clause 60. A removable segmentary shell according to any of clauses55-58, wherein the protrusions are provided on a labial surface of thesegmentary shell.

Clause 61. A removable segmentary shell according to any of clauses55-58, wherein the protrusions are provided on a lingual surface of thesegmentary shell.

Clause 62. A removable segmentary shell for being fitted on a segment ofteeth in a posterior lateral sector of the mandible, the segment ofteeth comprising between two and six adjacent teeth and extending from acanine or premolar to a premolar or molar, wherein the segmentary shellcomprises one or more protrusions having a sloping surface extendingbetween a base, and a top edge, the top edge being located closer to themaxilla than the base, wherein

the top edge is located distally with respect to the base.

Clause 63. A method for treating a malocclusion, including

fitting a removable segmentary shell to a segment of teeth in aposterior lateral sector of a maxilla or manible, the segment of teethcomprising between two and six adjacent teeth and extending from acanine or premolar to a premolar or molar,

fitting a complete fixating shell configured to fit over an arch ofteeth of the other of the maxilla and the mandible,

wherein the segmentary shell has a first surface and the completefixating shell has a corresponding second surface,

wherein the first surface comprises one or more first protrusions

and the second surface comprises one or more second protrusions,

wherein the first and second protrusions are shaped such that when thefirst and second protrusions enter into contact, the second protrusionsprovide a distalization force to the first protrusions.

Although only a number of examples have been disclosed herein, otheralternatives, modifications, uses and/or equivalents thereof arepossible. Furthermore, all possible combinations of the describedexamples are also covered. Thus, the scope of the present disclosureshould not be limited by particular examples, but should be determinedonly by a fair reading of the claims that follow.

1. An orthodontic system comprising: a removable segmentary shell forbeing fitted on a segment of teeth in a posterior lateral sector of anarch, the segment of teeth comprising between two and six adjacent teethand extending from a canine or premolar to a premolar or molar; and aresilient traction element, wherein the removable segmentary shellcomprises a labial retention feature configured to be coupled with theresilient traction element; and wherein the orthodontic system isconfigured to apply forces in a distal direction to the segment ofteeth, without transferring the forces to other teeth outside thesegment in the arch.
 2. The orthodontic system according to claim 1,wherein the resilient traction element is an elastic band.
 3. Theorthodontic system according to claim 2, wherein the labial retentionfeature for receiving the resilient traction element is a hook.
 4. Theorthodontic system according to claim 1, further comprising an anchorfor receiving the resilient traction element.
 5. The orthodontic systemaccording to claim 4, wherein the anchor is a bracket configured formounting on a tooth.
 6. The orthodontic system according to claim 1,wherein the segmentary shell comprises a first unilateral indent betweena first pair of teeth of the segment, wherein the first indent isoversized with respect to a space between the first pair of teeth, suchthat the first indent is compressed when the shell is positioned on thesegment of teeth.
 7. The orthodontic system according to claim 6,wherein the first unilateral indent is an indent on a labial side. 8.The orthodontic system according to claim 6, wherein the first pair ofteeth of the segment include a premolar and a first molar.
 9. Theorthodontic system according to claim 6, wherein the segmentary shellcomprises a second unilateral indent on a side opposite to theunilateral indent and between a second pair of teeth of the segment,wherein the second indent is oversized with respect to a space betweenthe second pair of teeth, such that the second indent is compressed whenthe shell is positioned on the segment of teeth.
 10. The orthodonticsystem according to claim 9, wherein the second pair of teeth of thesegment are a first molar and a second molar.
 11. The orthodontic systemaccording to claim 1, further comprising a fixating complete shellcovering a complete dental arch of either the maxilla or mandible. 12.The orthodontic system according to claim 1, comprising a series ofconsecutive segmentary shells, wherein the segmentary shells areconfigured to apply a corrective distal force to the segment of teeth,and wherein the consecutive segmentary shells of the series are shapedto correspond to consecutive positions of the segment of teeth in adesired treatment.
 13. The orthodontic system according to claim 12,wherein the series of consecutive segmentary shells are configured notto apply corrective forces other than forces in the distal direction tocanine or premolars.
 14. The orthodontic system according to claim 12,wherein one or more shells of the series of segmentary shells areconfigured to apply a rotational force to a molar around a palatal rootof the molar, wherein optionally the molar is a first molar.
 15. Theorthodontic system according to claim 1, wherein the segment extendsfrom a canine to a molar.
 16. An orthodontic system comprising: aremovable segmentary shell for being fitted on a segment of teeth in aposterior lateral sector of an arch, the segment of teeth comprisingbetween two and six adjacent teeth and extending from a canine orpremolar to a premolar or molar; and a resilient traction element,wherein the removable segmentary shell comprises an opening for fittingaround a labial retention feature provided on a tooth of the segment ofteeth, the labial retention feature configured for receiving theresilient traction element, and wherein the orthodontic system isconfigured to apply forces in a distal direction to the segment ofteeth, without transferring the forces to other teeth outside thesegment in the arch.
 17. The orthodontic system according to claim 16,wherein the segmentary shell is substantially transparent ortranslucent.
 18. The orthodontic system according to claim 16, whereinthe resilient traction element is an elastic band.
 19. The orthodonticsystem according to claim 18, wherein the labial retention feature forreceiving the resilient traction element is a hook.
 20. The orthodonticsystem according to claim 16, wherein the segmentary shell comprises afirst unilateral indent on a labial side between a premolar and a molarof the segment, wherein the first indent is oversized with respect to aspace between the premolar and the molar, such that the first indent iscompressed when the shell is positioned on the segment of teeth.